I have an SWC as well as the 50mm Distagon for the 500 series, and have the correct screw-in shades for both. The 38 hood is exactly the same as the 50 hood, except that it is 3mm shorter in depth. I've seen claims that the one for the 50mm will work fine for the SWC but I haven't ever tried it myself. There are several hoods for the 50mm Distagon C lens on ebay at the moment (original Hasselblad items) going for around $40. You could get one of those and try it, perhaps grind it down by 3mm if necessary.